J. Mater. Environ. Sci. 6 (4) (2015) 997-1003 ISSN : 2028-2508 CODEN: JMESCN
Boudanga et al.
Growth and nodulation in faba bean-rhizobia symbiosis under different soil phosphorus levels: acid phosphatase and phosphorus deficiency tolerance L. Boudanga▲1, M. Farissi▲1, A. Bouizgaren2, C. Ghoulam*1 1
Unit of Plant Biotechnology and Symbiosis Agro-physiology, Faculty of Sciences and Techniques, PO. Box 549, Gueliz, 40000 Marrakesh, Morocco 2 Unit of Plant Breeding, National Institute for Agronomic Research (INRA), PO. Box 533, Gueliz 40000, Marrakesh, Morocco.
Received 25 Aug 2014, Revised 3 Dec 2014, Accepted 3 Dec 2014 * Corresponding Author. E-mail:
[email protected] ; Tel: (+212(0)668730172) ▲
These authors contributed equally to this work.
Abstract The symbiosis faba bean-rhizobia behaviors under different soil phosphorus levels were studied. The plants were grown under symbiotic nitrogen fixation without fertilizers application. At flowering and maturity stages, ten plants per site were harvested and analyzed for their growth and nodulation, phosphorus and nitrogen contents. The acid phosphatases activity was analyzed in nodules and rhizospheic soils. Results showed that the nodular and shoot dry biomass were associated to the richness of the soil in available phosphorus. The highest and significant dry biomass was noted in plants of site 2 having a highest level in soil available phosphorus (85 and 0.66 g .plant-1 for shoots and nodules respectively) while the lowest values were noted with the plants of site 3 (43.75 and 0.43 g .plant-1 for shoots and nodules) showing the smallest soil available phosphorus. The P contents were associated with the soil P availability. The highest values were noted in plants of site 2 (11.46 mg P. g DW-1 for shoots and 19.50 mg P. g DW-1 for nodules). The amounts of nitrogen accumulated ranged from 2.51 to 4.37 mg . g DW-1 in shoots and from 3.36 to 6.01 mg . g DW-1 in nodules. The soil phosphorus level influenced the potassium sorption. Low levels of soil available phosphorus accentuated the enzymatic activity of acid phosphatase in nodules and rhizospheric soil. The increase in acid phosphatases activity could be an adaptation mechanism developed by faba bean plants for tolerance to phosphorus deficiency stress. Keywords: Faba bean, Growth, Nodulation, Phosphorus, Acid phosphatase
Introduction Legumes are a major source of protein and vegetable oils. They are widely cultivated throughout the world [1]. In Mediterranean area, these plants occupy an important place due to their agro-economic and environmental interests. Indeed, leguminous plants have a very favorable influence on soil fertility by contributing to the incorporation of nitrogen in ecosystems offering thus beneficial, ecological and economical impacts, helping to reduce or limit the use of chemical fertilizers by nitrogen-fixing symbiosis involving rhizobial strains [2]; [3]. However, in arid and semi arid areas, legume-rhizobia symbiosis is negatively affected by many environmental constraints, such as water deficit, salinity, temperature variations and soil deficiency in inorganic nutrients particularly available phosphorus for plants [4]; [5]; [6]; [7]; [8]; [9]. Indeed phosphorus (P) is a key nutrient limiting the productivity of legumes [10]. The majority of the phosphorus contained in the soil is in inorganic and organic complex forms. These forms are not directly usable by the plants [11]. Indeed, the high reactivity of P with iron, aluminum and calcium, to form insoluble compounds, reduces its mobility in the soil solution. These reactions provoked a very low P availability and low efficiency of phosphate fertilizers used by plants [12]. Nutritional deficiency related to soil P low availability is the major factor limiting symbiotic nitrogen fixation process [10], root growth, the process of photosynthesis, translocation of sugars and other functions [12].
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J. Mater. Environ. Sci. 6 (4) (2015) 997-1003 ISSN : 2028-2508 CODEN: JMESCN
Boudanga et al.
Phosphorus deficiency also affects the growth of rhizobia [4] and reduces the growth of nodules [10];[13]. In addition to phosphorus demand of the host plant, nodules require larger amounts of P than other plant tissues [14]. Morphological responses to phosphorus deficiency involve altering root architecture, mainly by a decrease of the primary root growth and increased lateral root number and the formation of root hairs [15]; [16]. Physiological and biochemical responses include changes in carbon metabolism, synthesis and secretion of phosphatases and phytases, exudation of organic acids (citrate, malate), and improving the expression of high affinity phosphate transporter [17]; [15]; [16]. The phosphatases are enzymes involved in the recovery of phosphate trapped in organic molecules allowing thus the improvement of symbiosis P nutrition. In this context, the present work aims to evaluate the behavior of faba bean-rhizobia symbiosis under phosphorus deficiency through monitoring the plots with different levels of soil available Pi. The evaluation focused the growth and nodulation and some physiological and biochemical properties associated with phosphorus deficiency tolerance as phosphatase acid (APase) activity.
2. Materials and methods 2.1. Site description and growth conditions The present study was carried out at four small farmers’ fields in a semi arid zone of Haouz area (Tamazouzt) at the region of Marrakesh (sub-centre of Morocco) with the following geographical coordinates: Altitude: 631 m - Latitude: 31°38’08’’.2, North-Longitude: 7°45’41’’West. The soil available P was determined for the plot prior to culture installation. The experiments were conducted during 2011. The trial’s management was the same as applied locally and plants were grown under symbiotic nitrogen fixation without chemical fertilizers application. The plants were irrigated once a week using a gravity irrigation system. The evaluation of the plots was performed by sampling 10 plants per site and soil samples. In the laboratory, the samples were subjected to different analyzes. 2.2. Soil Analyses Soils characterization was based on measuring of many physical and chemical parameters. The soil pH was determined with a pH meter using a portion of 10 g of soil and 25 ml of distilled water for pH water. For pH KCl, 25 ml KCl (1 mol.L-1) and 25 ml of distilled water were used. The electrical conductivity (EC) was determined with a conductivimeter using an aqueous extract of soil (20 g of soil sample in 100 ml of distilled water). Total P was determined after igniting air dried soil samples at 550 °C for 4 h and dissolving the ashed samples in concentrated HCl. The soil available P (Olsen P) to plants was determined after extraction in 0.5 M NaHCO 3 [18]. Available and total P were analyzed by the molybdate blue method by reading the absorbance at 820 nm after color development at 100 °C for 10 min [19]. Sodium (Na +) and potassium contents (K+) were determined using a flame spectrophotometer Jenway type [20]. Soil physicochemical properties of all sites studies were presented in Table 2. 2.3. Plant and nodular dry weights Ten plants were sampled from each site and separated to shoots and nodulated roots. Roots and nodules were carefully separated from rhizospheric soil, washed through a sieve and then the nodules were detached. This allows to retrieve as maximum as possible of nodule and root biomass from the detached rhizospheric soil. Shoots and nodules were dried at 70 °C for 3 days to determine their dry weights and thereafter dry samples were ground to enable determination of P and N contents. 2.4. APase activity in rhizosphere soils The nodulated roots were dug to 20 cm depth and the adhered soil layers (~2 mm) were collected and designated as rhizosphere soil [6]. All the soil samples were first sieved (
